PHP - Is there a way to get a variable value if it is set?

Question

I always find myself writing something like:

if(isset($var))
{
    DoSomethingWith($var);
}
else
{
    DoSomethingWith(null);
}

or

if(isset($arr["key"]))
{
    DoSomethingWith($arr["key"];
}
else
{
    DoSomethingWith(null);
}

My question is exacly this:

Is there a way to write a get_var_if_set() function so that you can simply write...

DoSomethingWith(get_var_if_set($var));
/// and
DoSomethingWith(get_var_if_set($arr["key"]));

....WITHOUT notifying if $var doesn't exists or that $arr doesn't have a set value for "key"?

I guess it should be something like this:

function get_var_if_set($a)
{
    return (isset($a) ? $a : null);
}

But that doesn't work because calling get_var_if_set() with unset variables will always generate a Notice, so it might need a little magic.

Thanks all folks.

Edit A user who deleted his answer suggested to pass variables by reference, as PHP will pass null if the $variable doesn't exist.

So that would be perfect, take a look at these solutions (which might probably be equivalent):

function get_var_if_set(&$a) { return (isset($a) ? $a : null); }
function get_var_if_set(&$a) { return $a ?? null; } // Only in PHP 7.0+ (Coalescing operator)

Note: Coalescing operator suggested by Koray Küpe

The problem as you can see is that they initialize the passed variables somehow in the return statement. We don't want that.

In a new document, compare `echo $a;` vs `echo @$a;`. Although I think suppressing errors is generally not a good thing at all. — Lucas Krupinski, May 08 '17 at 12:16
You can simply use: `DoSomethingWith($var??null);` or `DoSomethingWith($var?:null);` — Thamilhan, May 08 '17 at 12:16
@LucasKrupinski what is the use of `@` in front of a variable? — Antonios Tsimourtos, May 08 '17 at 12:17
@AntonisTsimourtos - `@` [suppresses errors](http://stackoverflow.com/questions/1032161/what-is-the-use-of-the-symbol-in-php) — Lucas Krupinski, May 08 '17 at 12:18
@AntonisTsimourtos it is used to suppress errors and warnings — Ndroid21, May 08 '17 at 12:18
function get_var_if_set($a=null) { return $a; } May be this is what you want to do here the function set the default value of argument to null so if you enter value it will be returned else the function return null , But is that useful — Osama, May 08 '17 at 12:21
@LucasKrupinski in fact I didn't want to suppress by using that @! — J. Brown, May 08 '17 at 12:22
@sunilwananje I also didn't want that extra operation! But thanks both for playing! =) — J. Brown, May 08 '17 at 12:22

score 4 · Answer 1 · answered May 08 '17 at 12:18

4

If you use PHP 7.0+ you can use null coalescing operator.

return $a ?? null;

Note: The operator checkes whether the variable exist and not empty. So, if the variable is already set but empty, it will return the null variable already.

answered May 08 '17 at 12:18

Koray Küpe

716
6
24

That's smart, but [it does spit out notifications](https://eval.in/789705)! The problem is when you execute _call_a_function_with($some_unexistent_parameter);_ PHP gets angry. I want a "magic function" that tells PHP "It doesn't matter what I'm passed, nor if it exists or not, I'm built to handle undefined indexesand unknown variables." – J. Brown May 08 '17 at 13:14

score 0 · Answer 2 · answered May 08 '17 at 12:18

0

The problem is not the var itself, but the key of the array key in this:

DoSomethingWith(get_var_if_set($arr["key"]))

So the only solution is to check for the array and the key you're looking for.

function get_var_if_set($a, $key = null)
{
    if(is_array($a) && array_key_exists($key, $array)) {
        return $a[$key]; 
    } else {
          return (isset($a) ? $a : null);
    }
}

answered May 08 '17 at 12:18

napolux

15,574
9
51
70

The coolness of the function isset() is that you can give it things that don't exist, and at most you will get false; PHP knows isset() might receive inexistent variables and it doesn't notify it. I want sort of wrapper-function for isset, that gives you directly [value or null], not [true or false]. Your solution ignores the problem that if you call get_var_if_set($inexistent_var), PHP tells you (with a notice) that $inexistent_var doesn't exist. – J. Brown May 08 '17 at 13:47

PHP - Is there a way to get a variable value if it is set?

2 Answers2